Fire retardant epoxy resins containing 3-hydroxyalkylphosphine oxides

ABSTRACT

Epoxy resins are rendered fire retardant by the addition thereto of a 3-hydroxyalkylphosphine oxide. Other halogen containing flame retardants may or may not be present in the composition. Mixtures containing a brominated epoxide and/or a halogenated phosphine oxide provide a high level of flame retardance at low levels of the additive. The epoxy resins may be heat cured in the presence of an acid anhydride or amine to form a polymer having the phosphine oxide incorporated in the polymer molecule.

The present invention relates to thermosetting epoxy resin compositionswhich are rendered flame retardant by having combined therewith aneffective amount of a hydroxyalkylphosphine oxide.

The epoxide resins are well known and have been described in numerouspublications. To improve flame retardant characteristics, epoxy resinshave been compounded with phosphate and phosphonate esters includingthose containing haloalkyl groups as described in British Pat. No.1,487,609, U.S. Pat. No. 3,192,242 and South African Pat. No. 18201/77.The use of triphenylphosphine as a flame retardant additive for epoxyresins was described by Martin and Price, J. Applied Polymer Science,12, 143-158 (1968).

Tetrakishydroxymethylphosphonium chloride and trishydroxymethylphosphineoxide have also been used in epoxy resins as described in U.S. Pat. No.2,916,473, and aminoalkylphosphonic acid esters are suggested as fireretardant hardeners for epoxy resins in U.S. Pat. No. 4,151,229.

The Maier U.S. Pat. Nos. 3,666,543 and 3,716,580 disclose2-hydroxyalkylphosphine oxides and halogenated derivatives thereof thatare said to have utility as flameproofing agents. However, the knownflame retardant additives for epoxide resin compositions suffergenerally from one or more deficiencies including low compatibility, lowthermal stability, or poor fire retardant behavior.

In accordance with the present invention, it has now been discoveredthat the addition of a small but effective amount of a3-hydroxyalkylphosphine oxide to an epoxy resin will increase itsresistance to burning. The 3-hydroxyalkylphosphine oxides may be usedwith either amine or anhydride hardeners and they may be used alone orin combination with halogen, and especially bromine, containing epoxideresins. When the epoxide resin is heat cured in the presence of the3-hydroxyalkylphosphine oxide and an anhydride or amine hardener, thephosphine oxide is believed to react with the hardener and/or terminalepoxy groups to become incorporated in the polymer molecule. Usefulphosphine oxides that impart fire resistance to epoxy resins are thosephosphine oxides having the general formula: ##STR1## wherein R₁ may bethe same or a different radical selected from the group consisting ofhydrogen, phenyl, hydroxymethyl and alkyl radicals of 1-4 carbon atoms,R₂ may be the same or a different radical selected from the groupconsisting of hydrogen, hydroxymethyl, and alkyl radicals of 1-4 carbonatoms, R₃ may be the same or a different radical selected from the groupconsisting of hydrogen and methyl radicals; R₄ is an alkyl radical of2-8 carbon atoms and n is either 0 or 1. Particularly effectivephosphine oxide additives for increasing the fire resistance of epoxideresin are tris(3-hydroxypropyl)phosphine oxide,tris(2-methyl-3-hydroxypropyl)phosphine oxide, sec-butylbis(3-hydroxypropyl)phosphine oxide and mixtures of the same. Suchpreferred phosphine oxides may be conveniently prepared by reactingphosphine with allyl alcohol and/or methallyl alcohol followed byoxidation of the resulting tertiary phosphine. To prepare mono sec-butylphosphine oxide, the phosphine is first reacted with butene followed bythe addition of allyl alcohol.

Suitable 3-hydroxyalkylphosphine oxides for use as fire retardants inthe present invention may also be prepared by reacting phosphine withother commercially available alcohols such as 1-butene-3-ol,2-butene-1-ol, 2-heptene-1-ol, cinnamyl alcohol, 2-butyl-2-propene-1-ol,butene-2-diol 1,4 and 2-hydroxymethyl propene-1-ol-3.

Although any of the known hardeners for epoxy resins may be used inconjunction with the phosphine oxide flame retardant additives, theamine and anhydride hardeners are particularly preferred. The3-hydroxyalkylphosphine oxides may, if desired, be reacted with atypical cyclic dicarboxylic acid anhydride such as phthalic anhydride,nadic methyl anhydride, etc., to form an intermediate ester which willfurther react in an epoxy resin system to produce a cured flameretardant object. Alternatively, the 3-hydroxyalkylphosphine oxides maybe reacted with the epoxy resin monomers such as epichlorohydrin withelimination of hydrochloric acid to give a glycidyl ether derivative.Such intermediates would have excellent compatibility with epoxy resinsand minimize the reaction between the hardener and the three hydroxygroups of the phosphine oxide.

Alternatively, the 3-hydroxyalkylphosphine oxides may be mixed with orpartially reacted with the uncured epoxy resins followed by addition ofthe hardener, anhydrides or amines to cure the resin.

Other suitable hardeners for the epoxy resins containing3-hydroxyalkylphosphine oxides are the aromatic amines such as methylenedianiline or other amines such as dicyandiamide or other highertemperature curing agents such as 4,4' diaminodiphenyl sulfone, or BF₃-monoethylamine complex.

The particular epoxy resin and the specific hardener that is used arenot critical as the hydroxyalkylphosphine oxides herein described willreact with all of the known epoxy resins. The hardeners employed neednot be limited to those mentioned above as all hardeners common to epoxyresin technology may be used to obtain the fire retardant epoxy resinsof the present invention.

It will be understood that if the functionality of the epoxy resinand/or the phosphine oxide and/or the hardener is three or greatercrosslinking may occur with the production of infusable molded objectswhereas when the functionality of the phosphine oxide, epoxy resins andanhydride or amine is two or less, thermoplastic resins are obtained.

Mixtures may be prepared of the 3-hydroxyalkylphosphine oxides andhardeners prior to addition of the epoxy resin monomer. Such phosphineoxide-hardener intermediate may be prepared by heating the phosphineoxide with, for example, anhydrides at a temperature between 70° C. and120° C. until a solution forms. Mixed anhydrides such as mixtures ofphthalic anhydride and nadic methyl anhydride in all proportions may beused. The phosphine oxide may be present in amounts up to 25% by weightor more in the final resin formulation but is optimally present inamounts from about 5% to about 20% by weight based upon the weight ofepoxide present. When anhydrides are used as the hardener,stoichiometric amounts are preferred, i.e., the ratio of the moles ofdibasic anhydride to the equivalents of epoxide is desirably from about0.80 to about 1.2. Optimally, the ratio of the moles of anhydride to theequivalents of epoxide is between about 0.90 and about 1.0.

In those cases where the solubility of the 3-hydroxyalkylphophine oxidein the epoxy resin monomers is not a problem, the phosphine oxide can bemixed with the epoxy resin first, an anhydride hardener first, or allthree can be mixed at once. The 3-hydroxyalkylphosphine oxides werefound to have an accelerating effect upon the cure of epoxy resins suchthat no additional accelerators are required.

The resin mixtures herein described were cast into sheets by heating inmolds consisting of mylar-lined glass plates with teflon spacers.Fillers may be added to the resin-phosphine oxide mixtures which canthen be compression, transfer or injection molded. The epoxy resinmixtures of the present invention can also be used as laminating resinsusing either dry molding or wet lay-up techniques. The preferredsubstrate is glass cloth but a woven or non-woven fabric or sheets ofcellulose may be substituted for the glass cloth to obtain a laminatehaving different physical and electrical properties. Such epoxy resinscan be used in any application involving epoxy resins but are mostsuited for electrical applications including laminated printed circuitboards, potting compounds, castings, encapsulations, molding powders,etc. The 3-hydroxyalkylphosphine oxide-epoxy resin compositions may alsobe used as coatings, sealants or adhesives, and can be used with orwithout fillers and other additives.

The physical and electrical properties of those epoxy resins cured inthe presence of phosphine oxide additives are essentially identical tothose epoxy resins containing no additives and the thermal propertiessuch as glass transition temperature, and heat distortion temperaturedid not vary substantially from those resins that contained no3-hydroxyalkylphosphine oxide. With the proper formulation and curingtemperature such variations, as do exist, may be made very small.

The 3-hydroxyalkylphosphine oxides described herein may be used as thesole flame retardant in epoxy resins or may be used in combination withother halogen-containing flame retardants. Especially effective aremixtures containing tris(3-hydroxypropyl)phosphine oxide in combinationwith a brominated bisphenol A based resin such as the diglycidyl etherof tetrabromobisphenol A (manufactured by the Dow Chemical Company ofMidland, Michigan under the trademark DER 542®).

The following Examples are intended to illustrate some of the morepreferred aspects of the present invention and, accordingly, should notbe considered as necessarily limiting the scope of the invention. Allparts are expressed in parts by weight unless otherwise specified.

EXAMPLE I

A mixture of tris(3-hydroxypropyl)phosphine oxide, 18.0 g (0.08 mole),phthalic anhydride, 30.0 g (0.20 mole) and 18.0 g (0.10 mole) of nadicmethyl anhydride were heated and stirred in a beaker under nitrogen toabout 120° C. for 15-20 minutes until a homogeneous solution formed. Themixture on cooling to room temperature was a viscous oil. This mixturewas again heated to 100° C. and 60 g (0.321 equivalents) of an epoxyresin derived from 2 moles of epichlorohydrin and 1 mole of2,2-bis(4-hydroxyphenyl)propane (bisphenol A) having a viscosity of 110to 150 poises and an equivalent weight of 185-192 (available from ShellDevelopment Company, Houston, Texas and identified as EPON 828®) wasadded. A solution quickly formed and the mixture was poured into twoflat TEFLON® molds (7.62 cm×12.7 cm×0.32 cm). TEFLON® is a vinylfluoride polymer manufactured by E. I. duPont deNemours and Co. ofWilmington, Delaware. The molds were placed in an oven, cured at 100° C.for 2 hours and post-cured at 160° C. for 3 hours. The pieces were hard,yellow glasses with a high gloss finish. These pieces were cut into 1.27cm wide strips for testing.

Samples were tested for flammability according to procedures establishedby the Underwriter Laboratories Bulletin No. 94, STANDARD FOR TESTS FORFLAMMABILITY OF PLASTIC MATERIALS FOR PARTS IN DEVICES AND APPLIANCES,Second Ed., Second Impression (as revised to Feb. 1, 1974) dated July30, 1976. The Vertical Burning Test for classifying materials 94 V-0, 94V-1, or 94 V-2 and described in Section 3 of this publication, was used.The average burn time for 10 ignitions was 3.8 seconds and the verticalburn test rating was V-0. The oxygen index determined by ASTM test D2863was 30.4. The glass transition temperature (Tg) as measured bydifferential scanning calorimetry was 88° C.

EXAMPLE II

Example I above was repeated except that thetris(3-hydroxypropyl)phosphine oxide was eliminated from the resinhardener mixture. The heat cured epoxy resin burns completely, has anoxygen index of 19.1 and a glass transition temperature, measured bydifferential scanning calorimetry, of 125° C.

EXAMPLE III

Example I was repeated except that 13.2 g (0.06 mole) oftris(3-hydroxypropyl)phosphine oxide was substituted for the 18 g (0.08mole) of tris(3-hydroxypropyl)phosphine oxide used in that Example. Theresulting composition had an oxygen index of 32.7. The average burn timefor 10 ignitions was 22 seconds and the vertical burn test rating wasV-1. The glass transition temperature, measured by differential scanningcalorimetry, was 108° C.

EXAMPLE IV

A mixture of 9.0 g (0.04 mole) of tris(3-hydroxypropyl)-phosphine oxide,27 g (0.18 mole) of phthalic anhydride, and 16.2 g (0.09 mole) of nadicmethyl anhydride, were heated and stirred in a beaker under nitrogen toabout 120° C. for 15-20 minutes until a homogeneous solution formed. Themixture on cooling to room temperature was a viscous oil. This mixturewas again heated to 100° C. and 60 g (0.321 equivalents) of the epoxyresin described above in Example I was added. A solution quickly formed,was cast in molds and cured in an oven for 2 hours at 100° C. followedby curing for an additional 3 hours at 160° C. The castings were cutinto 1.27 cm wide strips for testing. This product had an oxygen indexof 30.4. The average burn time for 10 ignitions was 4.6 seconds and thevertical burn test rating was V-0. The glass transition temperature,measured by differential scanning calorimetry was 113° C.

EXAMPLE V

A mixture of 60 g (0.321 equivalents) of the epoxide resin describedabove in Example I and 12.1 g (0.054 mole) oftris-(3-hydroxypropyl)phosphine oxide were heated at 170° C. for 90minutes under nitrogen until a solution formed. The solution was cooledto 100° C. and 45.0 g (0.304 mole) of phthalic anhydride was added. Theanhydride dissolved in 15 minutes with stirring and the mixture waspoured into a mold and cured at 100° C. for 3 hours, 135° C. for 2 hoursand finally 160° C. for 2.5 hours. The cured resin, when removed fromthe mold, was a hard, yellow glass having good physical characteristics.Mixtures made by this procedure have a shorter pot life than those madeby the procedure described in Example I above and care must be taken toavoid gel formation before the material is poured into the mold. Thecured resin has an average burn time of 4.7 seconds (V-0 rating by theUL-94 test), an oxygen index of 31, and the glass transition temperaturewas 120° C.

EXAMPLE VI

Sixty grams (0.321 equivalents) of the epoxide resin described above inExample I was weighed into a beaker with 30 g (0.20 mole) of phthalicanhydride, 18.0 g (0.10 mole) of nadic methyl anhydride and 18.0 g (0.08mole) of sec-butyl bis(3-hydroxypropyl)phosphine oxide. This mixture isheated at 120° C. under nitrogen and stirred for 30 minutes at whichtime all solids are dissolved in the solution. The liquid mixture wasthen cast in a mold consisting of two 0.64 cm thick pyrex glass plateslined with a polyethylene terephthalate film manufactured by E. I.duPont deNemours & Co. of Wilmington, Delaware under the trade nameMYLAR®. The MYLAR® film is 0.08 mm (3 mils) thick with 0.32 cm TEFLON®U-shaped spacer between the plates. The molds were placed in an oven at100° C. for 2 hours and the resin further cured at 160° C. for 3 hours.The cured resin, when removed from the mold, consisted of a hard,slightly yellow sheet 0.32 cm thick having an average burn time of 11.7seconds (UL-94 rating of V-1), an oxygen index of 31.8 and a glasstransition temperature of 95° C.

EXAMPLE VII

Ninety-five grams (0.48 equivalents) of the epoxide resin described inExample I above was heated with 19.0 g (0.084 mole) oftris(3-hydroxypropyl)phosphine oxide in a beaker at 160° C. undernitrogen for 1 hour with stirring. The solution so obtained was cooledto 80° C. and 27.0 g (0.135 mole) of bis(4-aminophenyl)methane (commonlyreferred to as methylene dianiline) was added. The mixture was furtherstirred and heated at 100° C. for 30 minutes at which time the methylenedianiline had gone into solution. This mixture was cast in the TEFLON®mold described in Example I and cured by heating in an oven at 100° C.for 3 hours and 200° C. for 1 hour. The product removed from the moldwas a hard, amber colored glass. It has a burn time of 2.7 seconds(UL-94 rating of V-O), an oxygen index of 31.3, and a glass transitiontemperature of 105° C.

EXAMPLE VIII

Example VII above was repeated except that thetris(3-hydroxypropyl)phosphine oxide was not added to the composition.The resulting product (containing no fire retardant) had an oxygen indexof 25.5 and burned to completion in the UL-94 vertical burn test. Theglass transition temperature of this product was 175° C.

EXAMPLE IX

A solution of 60 g (0.321 equivalents) of the epoxide resin described inExample I above, 18.0 g (0.08 mole) of tris(3-hydroxypropyl)phosphineoxide, and 54.0 g (0.30 mole) of nadic methyl anhydride was prepared asdescribed in Example I. A 60 g portion of this resin mixture was mixedwith 60 g of glass fibers in a two-roll mill which was heated to atemperature between 50° C. and 60° C. The glass fibers were well coatedafter 30 minutes and the material was removed from the mill. The glassfilled resin mixture was compression molded using a 5 cm disc mold and15 g of the glass filled resin at 300° F. for 40 minutes, thenincreasing the pressure to 9500 PSI. The product was removed from themold as a homogeneous 5 cm disc.

EXAMPLE X

The preceding Example IX was repeated except that no glass fibers wereadded to the resin composition. The electrical properties of the productso prepared are compared with the electrical properties of thecomposition containing glass fibers and described in Example IX aboveare compared in Table III.

EXAMPLE XI

The preceding Example was repeated except that notris(3-hydroxypropyl)phosphine oxide was added. The electricalproperties of this cured epoxy resin containing no fire retardantadditive are compared with the electrical properties of the curedproduct containing tris(3-hydroxypropyl)phosphine oxide with and withouta glass filler in Table III.

EXAMPLE XII

Eighty grams of the epoxide resin (0.428 equivalents) described inExample I above was heated and stirred with 16.0 g (0.071 mole) oftris(3-hydroxypropyl)phosphine oxide at 180° C. under nitrogen for 30minutes at which time all of the tris(3-hydroxypropyl)phosphine oxidehad dissolved. The solution was cooled to 110° C. and 3.0 g (0.04 mole)of dicyandiamide were added. This mixture was heated for 30 minutes at130° C. to dissolve the dicyandiamide and the resin was then poured intoa preheated mold consisting of two 20 cm×25 cm×0.64 cm pyrex glassplates lined with polyvinyl fluoride film manufactured by E. I. duPontdeNemours & Co. of Wilmington, Delaware under the trade name TEDLAR®.The two plates were separated by a 0.32 cm TEFLON® U-shaped spacer andheld together by C-clamps. The mold was placed in an oven at 200° C. for2.5 hours to cure. After curing, the mold was cooled and disassembledfor removal of a clear, hard, amber colored casting. The glasstransition temperature for this casting was determined, by differentialscanning calorimetry, to be 99° C.

EXAMPLE XIII

Example XII above was repeated except that 16.0 g (0.071 mole) ofsec-butyl bis(3-hydroxypropyl)phosphine oxide was substituted for 16.0 g(0.071 mole) of tris(3-hydroxypropyl)-phosphine oxide. The epoxide resincontaining the sec-butyl bis(3-hydroxypropyl)phosphine oxide anddicyandiamide was cast and cured at a lower temperature than wasemployed in Example XII (160° C.-170° C. for 3 hours). The resultingproduct had a glass transition temperature of 64° C.

EXAMPLE XIV

Example XII above was repeated except that 12.6 g (0.06 mole) oftris(3-hydroxypropyl)phosphine oxide was substituted for 16.0 g (0.071mole) of tris(3-hydroxypropyl)phosphine oxide. The cured resin had aglass transition temperature of 113° C.

EXAMPLE XV

A solution of 63.5 g (0.34 equivalents) of the epoxide resin of ExampleI above, 10.0 g (0.04 mole) of tris(3-hydroxypropyl)phosphine oxide and4.0 g (0.06 mole) of dicyandiamide was prepared as described in ExampleXII above.

In a separate beaker, 19.0 g (0.03 mole) of tetrabromobisphenol A and36.5 g (0.20 equivalents) of the epoxide resin described in Example Iabove were stirred and heated under nitrogen with 0.02 g of methyltris(3-hydroxypropyl)phosphonium chloride as catalyst to 150° C. Anexothermic reaction occurred with the temperature rising to 185° C. Thetemperature was maintained at 165° C. for 15 minutes and then cooled toroom temperature. This hard and friable solid was broken into smallpieces and added to the resin solution described in the first paragraphof this Example XV. This mixture was heated at 130° C. for 15 minutes atwhich time the mixture became homogeneous and the mixture was thenpoured into a preheated mold of the type described in Example XII above.The mold was placed in an oven at 200° C. for 2 hours, cooled, andopened to give a hard, clear, amber casting having a glass transitiontemperature of 122° C. when measured by differential scanningcalorimetry.

EXAMPLE XVI

Thirty-six and one-tenth grams (0.19 equivalents) of the epoxide resindescribed in Example I above was heated and stirred with 7.25 g (0.03mole) of tris(3-hydroxypropyl)phosphine oxide at 180° C. under nitrogenfor 30 minutes at which time all of the tris(3-hydroxypropyl)phosphineoxide had dissolved. The solution was cooled to 110° C. and 3 g (0.04mole) of dicyandiamide were added. This mixture was heated for 30minutes at 130° C. to dissolve the dicyandiamide.

In a separate beaker, 8.32 grams (0.015 mole) of tetrabromobisphenol Aand 15.98 g (0.085 equivalents) of the epoxide resin described inExample I above were stirred and mixed under nitrogen with 0.01 g ofmethyl tris(3-hydroxypropyl)phosphonium chloride as catalyst to 150° C.An exothermic reaction occured with the temperature rising to 185° C.The temperature was maintained at 165° C. for 15 minutes. The mixturewas then cooled to about 100° C. and 27.9 g (0.15 equivalents) of theepoxide resin described in Example I above was added and mixed to form ahomogeneous solution. The resin solution was added to the resincomposition described in the first paragraph of this Example and cast ina predetermined mold and cured at 200° C. for 2 hours. The cured productwas a hard, amber glass having a glass transition temperature of 121° C.

EXAMPLE XVII

Two hundred grams of the resin solution containingtris(3-hydroxypropyl)phosphine oxide and dicyandiamide prepared asdescribed in Example XII above was heated at 110° C. for 30 minutesafter the dicyandiamide had gone into solution and poured into a metalpan 15 cm in diameter. Nine pieces of glass cloth measuring 15 cm×10 cmand manufactured by Burlington Mills of Altavista, Virginia; (style7628/50/97 with I399 finish) were dipped into the resin to thoroughlycover the cloth and hung in an oven at 185° C. for 4-5 minutes. Theprepregs which were no longer tacky, were then taken from the oven andfound to contain 38 weight percent resin. The prepregs were stapledtogether and pressed at 390° F. (199° C.) at 400 psi (2.76 MPa) for 1hour. The final laminate had a resin content of 37% and a glasstransition temperature of 94° C.

EXAMPLE XVIII

Four hundred grams of the epoxide resin (2.14 equivalents) described inExample I above was heated and stirred with 80.0 g (0.355 mole) oftris(3-hydroxypropyl)phosphine oxide at 180° C. under nitrogen for 30minutes at which time all of the tris(3-hydroxypropyl)phosphine oxidehad dissolved. The solution was cooled to 110° C. and 15.0 g (0.22 mole)of dicyandiamide were added. This mixture is heated for 30 minutes at130° C. to dissolve the dicyandiamide and the resin was then cooled anddissolved in a mixture of 100 g methylethyl ketone and 100 g of2-methoxyethanol.

Nine pieces of glass cloth measuring 15 cm×10.0 cm manufactured byBurlington Mills type 7628/50/97 with I399 finish were dried in an ovenat 200° C. for 1.5 hours; immersed in the resin solution described abovefor 30 seconds and dried in an oven at 180° C.-185° C. for 5 minutes.The resulting prepregs contained 40% resin and were not tacky. Theprepregs were stapled together and pressed at 390° F. (199° C.) and 400psi (2.76 MPa) for 1 hour between TEFLON® lined metal plates. The finallaminate contained 39% resin and its glass transition temperature is 98°C. The laminate has no visable air bubbles and was characterized byexcellent cohesive strength.

EXAMPLE XIX

A resin solution containing tetrabromobisphenol A (TBBP-A) was preparedby heating 100 g (0.53 equivalents) of the epoxide resin described inExample I above and 54 g (0.10 mole) of tetrabromobisphenol A with 0.1 gof methyl trishydroxypropyl phosphonium chloride (as catalyst) to 150°C. with stirring under nitrogen. An exothermic reaction ensued with thetemperature rising to 185° C. The temperature was maintained at 185° C.for 15 minutes and cooled to room temperature. The cooled resin, anamber glass, was broken into small pieces, and 71.2 g of this productwas dissolved in 21.6 g of acetone. To this solution was added 2.8 g(0.04 mole) of dicyandiamide dissolved in 13 g of dimethyl formamide. Aslight precipitate formed that dissolved when the solution was warmed to35° C.

Eight 7.6 cm×7.6 cm pieces of glass cloth were dipped into the resinsolution and dried at 150° C. for 6 minutes. These pieces contained 49%resin and were not tacky. These pieces were pressed at 340° F. (171° C.)and 200 psi (1.38 MPa) for 30 minutes. The laminate when cooled,contained 31% resin. The glass transition temperature was 124° C.

EXAMPLE XX

Forty-two and three-tenths grams (0.13 equivalents) of an epoxide resinderived from 2 moles of epichlorohydrin and 1 mole of2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane, commonly referred to astetrabromobisphenol A, having an epoxide equivalent weight of 305-355and a Durrans' softening point of 40° C.-55° C. (available from DowChemical Company, Midland, Michigan and identified as DER 542®) is mixedunder nitrogen at 120° C. with 55.8 g (0.30 equivalents) of the epoxideresin described above in Example I. To this resin mixture is added(under nitrogen) 40 g (0.27 mole) of phthalic anhydride and 24.1 g (0.14mole) of nadic methyl anhydride with stirring while maintaining thetemperature at 120° C. When the mixture becomes homogeneous, 0.5 g ofbenzyl dimethyl amine was added and the mixture is cast in a mold asdescribed in Example VI and cured at 100° C. for 2 hours and 160° C. for3 hours. The resulting yellow glass had an oxygen index of 32.7 and aglass transition temperature of 140° C.

EXAMPLE XXI

The proceding Example was repeated except that 9.7 g (0.03 equivalents)of the epoxy resin DER 542® was substituted for 42.3 g (0.13equivalents) of the DER 542® employed in the preceding Example and 74.4g (0.40 equivalents) of the epoxide of Example I was substituted for the55.8 g (0.30 equivalents) of that resin employed in the precedingExample. The oxygen index of this product was 23.5 and the glasstransition temperature was 140° C.

EXAMPLE XXII

Example XX above was repeated except that 19.9 g (0.06 equivalents) ofDER 542® was substituted for 42.3 g (0.13 equivalents) of that resin and68.6 g (0.37 equivalents) of the resin of Example I was substituted for55.8 g (0.30 equivalents) of that resin. The resulting product had anoxygen index of 26 and a glass transition temperature of 138° C.

EXAMPLE XXIII

Example XX above was repeated except that 30.8 g (0.09 equivalents) ofDER 542® was substituted for 42.3 g (0.13 equivalents) of that resin and62.4 g (0.33 equivalents) of the epoxide of Example I above wassubstituted for 55.8 g (0.30 equivalents) of that resin. The resultingproduct had an oxygen index of 29.3 and a glass transition temperatureof 130° C.

EXAMPLE XXIV

A mixture of 34.6 g (0.19 equivalents) of the epoxide resin described inExample I above, 5.9 g (0.026 mole) of tris(3-hydroxypropyl)phosphineoxide, 20.0 g (0.14 mole) of phthalic anhydride and 12.0 g (0.08 mole)of nadic methyl anhydride was stirred and heated under nitrogen at 110°C. until a homogeneous solution was formed. To this homogeneous resinmixture is added 8.9 g (0.03 equivalents) of the brominated epoxy resindescribed in Example XX above (DER 542®) and stirring was continueduntil the mixture was homogeneous. The resin mixture was cast in a moldand cured in an oven at 100° C. for 2 hours and 160° C. for 3 hours. Theproduct was a hard, yellow glass characterized by an oxygen index of34.3 and a glass transition temperature of 130° C.

EXAMPLE XXV

Example XXIV above was repeated with the following changes:

    ______________________________________                                        EPON 828®    36.5 g  (0.20 equivalents)                                   DER 542®     5.0 g   (0.015 equivalents)                                  tris(3-hydroxypropyl)                                                         phosphine oxide  2.9 g   (0.013 mole)                                         ______________________________________                                    

The cured product had an oxygen index of 28.8 and a glass transitiontemperature of 109° C.

EXAMPLE XXVI

Example XXIV above was repeated with the following changes:

    ______________________________________                                        EPON 828®    36.5 g  (0.20 equivalents)                                   DER 542®     5.2 g   (0.016 equivalents)                                  tris(3-hydroxypropyl)                                                         phosphine oxide  5.7 g   (0.025 mole)                                         ______________________________________                                    

The resulting product had a oxygen index of 31 and a glass transitiontemperature of 110° C.

EXAMPLE XXVII

Example XXIV above was repeated with the following changes:

    ______________________________________                                        EPON 828®    34.6 g  (0.019 equivalents)                                  DER 542®     8.4 g   (0.025 equivalents)                                  tris(3-hydroxypropyl)                                                         phosphine oxide  2.9 g   (0.013 mole)                                         ______________________________________                                    

The resulting product had an oxygen index of 30.7 and a glass transitiontemperature of 110° C.

                                      TABLE I                                     __________________________________________________________________________    3-HYDROXYPROPYL PHOSPHINE OXIDES IN EPOXY RESINS                              Example                   Anhydride.sup.2                                                                     Oxygen.sup.3                                                                       UL-94.sup.4                              Number                                                                             Additive                                                                           Wt. %                                                                             % P                                                                              Hardener.sup.1                                                                         Equivalents                                                                         Index                                                                              Rating                                                                            Average Burn Time                                                                       Tg (°C.)            __________________________________________________________________________    I    THPPO.sup.5                                                                        14.3                                                                              2.0                                                                              PA/NMA = 2                                                                             .95   30.4 V-0 3.8 seconds                                                                             88                         II   None --  -- PA/NMA = 2                                                                             .95   19.1 Burn          125                        III  THPPO.sup.5                                                                        10.7                                                                              1.5                                                                              PA/NMA = 2                                                                             .95   32.7 V-1 22.0 seconds                                                                            108                        IV   THPPO.sup.5                                                                         8.0                                                                              1.1                                                                              PA/NMA = 2                                                                             .85   30.4 V-0 4.6 seconds                                                                             113                        V    THPPO.sup.5                                                                        10.3                                                                              1.4                                                                              PA       .95   31.0 V-0 4.7 seconds                                                                             120                        VI   BHPPO.sup.6                                                                        14.3                                                                              2.0                                                                              PA/NMA = 2                                                                             .95   31.8 V-1 11.7 seconds                                                                            95                         VII  THPPO.sup.5                                                                        13.5                                                                              1.9                                                                              MDA.sup.7 (28 PHR)                                                                     --    31.3 V-0 2.7 seconds                                                                             105                        VIII None --  -- MDA.sup.7 (28 PHR)                                                                     --    25.5 Burn          175                        __________________________________________________________________________     .sup.1 PA = Phthalic anhydride; NMA = Nadic methyl anhydride                   .sup.2 Ratio of moles of anhydride/equivalents epoxide                       .sup.3 ASTM D 2863                                                            .sup.4 UL94 Vertical Burn Test  Rating and average burn times                 .sup.5 Tris(3hydroxypropyl)phosphine oxide                                    .sup.6 Secbutyl bis(3hydroxypropyl)phosphine oxide                            .sup.7 Methylene dianiline is bis(4aminophenyl)methane                   

                  TABLE II                                                        ______________________________________                                        3-HYDROXYPROPYL PHOSPHINE OXIDES IN EPOXY                                     RESINS CURED WITH DICYANDIAMIDE                                                               UL-94.sup.1                                                   Example                         Average                                       Number  Additive  Wt. %   Rating                                                                              Burn Time                                                                              Tg                                   ______________________________________                                        XII     THPPO.sup.3                                                                             16      V-0   2.8 seconds                                                                             99° C.                       XIII    BHPPO.sup.4                                                                             16      V-0   3.2 seconds                                                                             64° C.                       XIV     THPPO.sup.3                                                                             12.6    V-1   8.2 seconds                                                                            113° C.                       XV      THPPO.sup.3                                                                             7.5     V-0   1.0 seconds                                                                            122° C.                               TBBP--A.sup.2                                                                           21.7                                                        XVI     THPPO.sup.3                                                                             7.4     V-0   3.5 seconds                                                                            121° C.                               TBBP--A.sup.2                                                                           8.6                                                         XVII    TBBP--A.sup.2                                                                           35      V-0   1.0 seconds                                                                            124° C.                       ______________________________________                                         .sup.1 Rating and average burn time for 10 ignitions                          .sup.2 Tetrabromobisphenol A                                                  .sup.3 Tris(3hydroxypropyl)phosphine oxide                                    .sup.4 Secbutyl bis(3hydroxypropyl)phosphine oxide                       

                                      TABLE III                                   __________________________________________________________________________    EPOXY RESINS CONTAINING 3-HYDROXYPROPYLPHOSPHINE                              OXIDE - ELECTRICAL PROPERTIES                                                                                             Volume.sup.3                      Example                                                                            Additive                                                                             Hardener.sup.1                                                                     Filler                                                                              Dielectric Const..sup.2                                                                AC Dissipation Factor.sup.2                                                               Resistivity                       __________________________________________________________________________                                                (ohm-cm)                          IX   THPPO.sup.4                                                                          NMA  50% glass                                                                           100 cps 4.4                                                                            .0008                                              (13.6 wt. %)      10.sup.3 cps 4.4                                                                       .0039                                                                10.sup.4 cps 4.4                                                                       .0080                                                                10.sup.5 cps 4.3                                                                       .0171                                         X    THPPO.sup.4                                                                          NMA  None  100 cps 3.6                                                                            .0012       1.5 × 10.sup.16                  (13.6 wt. %)      10.sup.3 cps 3.6                                                                       .0042                                                                10.sup.4 cps 3.6                                                                       .0080                                                                10.sup.5 cps 3.5                                                                       .015                                          XI   Blank  NMA  None  100 cps 4.1                                                                            .0015         2 × 10.sup.15                                    10.sup.3 cps 4.1                                                                       .0023                                                                10.sup.4 cps 4.0                                                                       .0041                                                                10.sup.5 cps 3.8                                                                       .015                                          __________________________________________________________________________     .sup.1 NMA is nadic methyl anhydride                                          .sup.2 ASTM D 150                                                             .sup.3 ASTM D 257                                                             .sup.4 Tris(3hydroxypropyl)phosphine oxide                               

                                      TABLE IV                                    __________________________________________________________________________    EPOXY RESINS-USE OF BROMINE WITH 3-HYDROXYPROPYL                              PHOSPHINE OXIDE.sup.1                                                         Wt. %        Wt. %        UL-94.sup.3                                         Example                                                                            THPPO.sup.4                                                                        % P                                                                              DER 542®                                                                        % Br                                                                              OI.sup.2                                                                         Rating                                                                            Average Burn Time                                                                       Tg                                    __________________________________________________________________________    II   --   -- --    --  19.1                                                                             Burn          125° C.                        XX   --   -- 26    12  32.7                                                                             V-0 1.8 seconds                                                                             140° C.                        XXI  --   -- 6.2   3   23.5                                                                             Burn          140° C.                        XXII --   -- 13.0  6   26.0                                                                             V-1 25.0 seconds                                                                            138° C.                        XXIII                                                                              --   -- 19.5  9   29.3                                                                             V-1 5.9 seconds                                                                             130° C.                        XXIV 7.2  1.0                                                                              10.8  5   34.3                                                                             V-0 1.4 seconds                                                                             130° C.                        XXV  3.8  0.5                                                                              6.5   3   28.8                                                                             V-1 11.3 seconds                                                                            109° C.                        XXVI 7.2  1.0                                                                              6.5   3   31.0                                                                             V-0 2.5 seconds                                                                             110° C.                        XXVII                                                                              3.7  0.5                                                                              10.6  5   30.7                                                                             V-0 2.6 seconds                                                                             110° C.                        __________________________________________________________________________     .sup.1 The hardener used was phthalic anhydride and nadic methyl anhydrid     (2:1). The ratio of moles of anhydride to equivalents of epoxide was 0.95     .sup.2 Oxygen index ASTM D 2863.                                              .sup.3 UL94 test. Rating and average burn time for 10 ignitions.              .sup.4 Tris(3hydroxypropyl)phosphine oxide.                              

We claim:
 1. A fire retardant epoxy resin containing an effective amountof a 3-hydroxypropylphosphine oxide having the general formula: ##STR2##wherein R₁ may be the same or a different radical selected from thegroup consisting of hydrogen, phenyl, hydroxymethyl and alkyl radicalsof 1-4 carbon atoms, R₂ may be the same or a different radical selectedfrom the group consisting of hydrogen, hydroxymethyl, and alkyl radicalsof 1-4 carbon atoms, R₃ may be the same or a different radical selectedfrom the group consisting of hydrogen and methyl radicals, R₄ is analkyl radical of 2-8 carbon atoms and n is either 1 or
 2. 2. The fireretardant epoxy resin of claim 1 containing an effective amount oftris-(3-hydroxypropyl) phosphine oxide.
 3. A fire retardant epoxy resinof claim 1 containing an effective amount of tris-(2-methyl3-hydroxypropyl) phosphine oxide.
 4. A fire retardant epoxy resin ofclaim 1 wherein said epoxy resin is derived from a reaction of anepichlorohydrin with bisphenol A.
 5. The fire retardant epoxy resin ofclaim 1 wherein said epoxy resin contains tetrabromobisphenol A in thepolymer molecule.
 6. The fire retardant epoxy resin of claim 1 whichcontains an effective amount of a hardener.
 7. The fire retardant epoxyresin of claim 6 wherein said hardener is nadic methyl anhydride.
 8. Thefire retardant epoxy resin of claim 6 wherein said hardener is methylenedianiline.
 9. The fire retardant epoxy resin of claim 6 wherein saidhardener is dicyandiamide.
 10. A method of increasing the fireresistance of an epoxy resin which comprises adding thereto an effectiveamount of a 3-hydroxypropylphosphine oxide having the general formula:##STR3## wherein R₁ may be the same or a different radical selected fromthe group consisting of hydrogen, phenyl, hydroxymethyl and alkylradicals of 1-4 carbon atoms, R₂ may be the same or a different radicalselected from the group consisting of hydrogen, hydroxymethyl, and alkylradicals of 1-4 carbon atoms, R₃ may be the same or a different radicalselected from the group consisting of hydrogen and methyl radicals, R₄is an alkyl radical of 2-8 carbon atoms and n is either 1 or
 2. 11. Aglycidyl ether of 3-hydroxypropylphosphine oxide having the generalformula: ##STR4## wherein R₁ may be the same or a different radicalselected from the group consisting of hydrogen, phenyl, hydroxymethyland alkyl radicals of 1-4 carbon atoms, R₂ may be the same or adifferent radical selected from the group consisting of hydrogen,hydroxymethyl, and alkyl radicals of 1-4 carbon atoms, R₃ may be thesame or a different radical selected from the group consisting ofhydrogen and methyl radicals, R₄ is an alkyl radical of 2-8 carbon atomsand n is either 1 or
 2. 12. A mixture of a hardener for an epoxy resinand a 3-hydroxypropylphosphine oxide having the general formula:##STR5## wherein R₁ may be the same or a different radical selected fromthe group consisting of hydrogen, phenyl, hydroxymethyl and alkylradicals of 1-4 carbon atoms, R₂ may be the same or a different radicalselected from the group consisting of hydrogen, hydroxymethyl, and alkylradicals of 1-4 carbon atoms, R₃ may be the same or a different radicalselected from the group consisting of hydrogen and methyl radicals, R₄is an alkyl radical of 2-8 carbon atoms and n is either 1 or
 2. 13. Anepoxy resin composition that is liquid at elevated temperaturescomprising the reaction product of an epoxy resin and a3-hydroxypropylphosphine oxide having the general formula: ##STR6##wherein R₁ may be the same or a different radical selected from thegroup consisting of hydrogen, phenyl, hydroxymethyl and alkyl radicalsof 1-4 carbon atoms, R₂ may be the same or a different radical selectedfrom the group consisting of hydrogen, hydroxymethyl, and alkyl radicalsof 1-4 carbon atoms, R₃ may be the same or a different radical selectedfrom the group consisting of hydrogen and methyl radicals, R₄ is analkyl radical of 2-8 carbon atoms and n is either 1 or 2; said epoxyresin composition having dissolved therein dicyandiamide.
 14. An epoxyresin composition comprising the reaction product of an epoxy resin withtetrabromobisphenol A and a 3-hydroxypropylphosphine oxide having thegeneral formula: ##STR7## wherein R₁ may be the same or a differentradical selected from the group consisting of hydrogen, phenyl,hydroxymethyl and alkyl radicals of 1-4 carbon atoms, R₂ may be the sameor a different radical selected from the group consisting of hydrogen,hydroxymethyl, and alkyl radicals of 1-4 carbon atoms, R₃ may be thesame or a different radical selected from the group consisting ofhydrogen and methyl radicals, R₄ is an alkyl radical of 2-8 carbon atomsand n is either 1 or 2.